1. Field of the Invention
The invention relates to a converter for the production of steel from solid and/or liquid charging substances, such as pig iron and/or scrap and/or sponge iron, comprising a refractorily fined refining vessel, a refining means feeding oxygen or an oxygen-containing gas and a heating means, as well as to a process for producing steel.
2. Description of the Related Art
It is already known (AT-B-232.531) to supply missing heat to the charging substances by means of burners in order to attain the desired tapping temperature or to selectively increase the scrap charge, wherein a blast pipe including an oxygen blowing pipe and a fuel supply pipe is provided as a heating-refining means. Through the fuel supply pipe, oil or natural gas, i.e., a fossil fuel, is injected into the refining gas.
It is true that by this known arrangement the scrap charge may be increased, yet also the required charging time increases with the scrap portion, because the flame must work itself through the scrap charged, which is present above the molten pig iron. The oxygen supplied does not ignite before the flame has smelted sufficient scrap as far as to the pig iron bath level, which takes a relatively long time.
From AT-B-372.110 a converter for the production of steel from solid and liquid charging substances, such as pig iron and scrap, is known, which comprises a heating-refining means, wherein the heating-refining means is comprised of a plasma burner, a jacket surrounding the plasma burner and destined for supplying oxygen, as well as a cooling jacket surrounding this jacket. A converter comprising a plasma burner provided for smelting scrap, furthermore, is known from U.S. Pat. No. 3,316,082, wherein a central oxygen-gas introduction is provided. A furnace including a water-cooled tungsten burner and an oxyen supply duct, furthermore, is known from U.S. Pat. No. 3,556,771.
By these known plasma heating means and tungsten electrodes, respectively, an additional energy supply is feasible; yet, frequent leakages occur on account of the water cooling of the plasma cathodes, which result in unbearable losses of productivity and high maintenance costs. The problem of leakages occurring is particularly aggravated if oxygen blowing is performed at the same time the plasma burner is set in operation. A further problem with such burners resides in that the amount of energy supplied is limited upwardly, because the water cooling conducts away a major part of the thermal energy.
From EP-A-0 257 450 an electric arc furnace is known, in which the supply of carbonaceous fuels and oxygen-containing gases is provided for the purpose of saving energy. The oxygen is injected obliquely downwards into the furnace through blowing means fixedly arranged in the upper furnace region. The gas flow forming sucks in the reaction gases derived from the scrap and the melt forming, and bums the same. With this electric arc furnace, an accordingly increasing charge of coal is required with an increased charge of scrap. This means that--similar to AT-B-232.531--electric energy is replaced with fossil energy in order to reach higher production outputs. This involves metallurgical drawbacks, such as increased N, H and S contents. Another disadvantage is in that the charging time (tap-to-tap time) is very long with electric arc furnaces due to a totally different melt control technology (flat bath) as compared to converter technology.
From AT-B-376.702 a metallurgical vessel is known, through whose ceiling several hollow electrodes are guided in each of whose cavities one gas feeding tube is guided in a liftable and lowerable manner. For the purpose of metallurgical treating of the most diverse steel grades, that vessel facultatively may be operated:
a) as an electric arc furnace for smelting charging substances and/or fluxes, by retracting the tube mouth to behind the mouth of the hollow electrode, PA1 b) as a plasma furnace for melting charging substances or fluxes at an elevated energy input, by displacing the tube mouth as far as to, or slightly in front of, the mouth of the hollow electrode and simultaneously feeding a plasma-generating gas, or PA1 c) as a refining converter, by displacing the tube mouth to beyond the mouth of the hollow electrode, if desired, until immersion in a bath of the molten charging substances and feeding an oxygen-containing gas while interrupting the current supply.
Since the introduction of electric energy is not possible during the blowing procedure, substantially more carbon than is required with common melting must be added to the charged scrap also in that case, which, again, involves the disadvantages described above.
In addition, the combined electrode and gas feeding tube liftable and lowerable in a cavity of the electrode involve great mechanical expenditures. There is the danger that the movability of the gas feeding tube relative to the electrode, in particular, the constant precise readjustment of the gas feeding tube, cannot be maintained due to the extensive heat caused by the plasma gas and due to the risk of contamination.